inner planets

two martian moons

Mars has two very small, irregular moons, Phobos (seen in Figure 25.18) and Deimos. These moons were discovered in 1877. They are named after the two sons of Ares, who followed their father into war. The moons were probably asteroids that were captured by Martian gravity.

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a red planet

Viewed from Earth, Mars is red. This is due to large amounts of iron in the soil. The ancient Greeks and Romans named the planet Mars after the god of war. The planets red color reminded them of blood. Mars has only a very thin atmosphere, made up mostly of carbon dioxide.

surface features

Mars is home to the largest volcano in the solar system. Olympus Mons is shown in Figure 25.16. Olympus Mons is a shield volcano. The volcano is similar to the volcanoes of the Hawaiian Islands. But Olympus Mons is a giant, about 27 km (16.7 miles/88,580 ft) tall. Thats three times taller than Mount Everest! At its base, Olympus Mons is about the size of the entire state of Arizona. Mars also has the largest canyon in the solar system, Valles Marineris (Figure 25.17). This canyon is 4,000 km (2,500 miles) long. Thats as long as Europe is wide! One-fifth of the circumference of Mars is covered by the canyon. Valles Marineris is 7 km (4.3 miles) deep. How about Earths Grand Canyon? Earths most famous canyon is only 446 km (277 miles) long and about 2 km (1.2 miles) deep. Mars has mountains, canyons, and other features similar to Earth. But it doesnt have as much geological activity as Earth. There is no evidence of plate tectonics on Mars. There are also more craters on Mars than on Earth. Buy there are fewer craters than on the Moon. What does this suggest to you regarding Mars plate tectonic history?

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mars

Mars, shown in Figure 25.15, is the fourth planet from the Sun. The Red Planet is the first planet beyond Earths orbit. Mars atmosphere is thin compared to Earths. This means that there is much lower pressure at the surface. Mars also has a weak greenhouse effect, so temperatures are only slightly higher than they would be if the planet did not have an atmosphere. Mars is the easiest planet to observe. As a result, it has been studied more than any other planet besides Earth. People can stand on Earth and observe the planet through a telescope. We have also sent many space probes to Mars. In April 2011, there were three scientific satellites in orbit around Mars. The rover, Opportunity, was still moving around on the surface. No humans have ever set foot on Mars. NASA and the European Space Agency have plans to send people to Mars. The goal is to do it sometime between 2030 and 2040. The expense and danger of these missions are phenomenal.

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motion and appearance

Venus is the only planet that rotates clockwise as viewed from its North Pole. All of the other planets rotate counterclockwise. Venus turns slowly, making only one turn every 243 days. This is longer than a year on Venus! It takes Venus only 225 days to orbit the Sun. Because the orbit of Venus is inside Earths orbit, Venus always appears close to the Sun. You can see Venus rising early in the morning, just before the Sun rises. For this reason, Venus is sometimes called the morning star. When it sets in the evening, just after the Sun sets, it may be called the evening star. Since planets only reflect the Suns light, Venus should not be called a star at all! Venus is very bright because its clouds reflect sunlight very well. Venus is the brightest object in the sky besides the Sun and the Moon.

volcanoes

Venus has more volcanoes than any other planet. There are between 100,000 and one million volcanoes on Venus! Most of the volcanoes are now inactive. There are also a large number of craters. This means that Venus doesnt have tectonic plates. Plate tectonics on Earth erases features over time. Figure 25.13 is an image made using radar data. The volcano is Maat Mons. Lava beds are in the foreground. Scientists think the color of sunlight on Venus is

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oceans and atmosphere

Earth is a very diverse planet, seen in Figure 25.14. Water appears as vast oceans of liquid. Water is also seen as ice at the poles or as clouds of vapor. Earth also has large masses of land. Earths average surface temperature is 14C (57F). At this temperature, water is a liquid. The oceans and the atmosphere help keep Earths surface temperatures fairly steady. Earth is the only planet known to have life. Conditions on Earth are ideal for life! The atmosphere filters out harmful radiation. Water is abundant. Carbon dioxide was available for early life forms. The evolution of plants introduced more oxygen for animals.

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earth

Earth is the third planet out from the Sun, shown in Figure 25.14. Because it is our planet, we know a lot more about Earth than we do about any other planet. What are main features of Earth?

extreme temperatures

Mercury is very close to the Sun, so it can get very hot. Mercury also has virtually no atmosphere. As the planet rotates very slowly, the temperature varies tremendously. In direct sunlight, the surface can be as hot as 427C (801F). On the dark side, the surface can be as cold as 183C (297F)! The coldest temperatures may be on the insides of craters. Most of Mercury is extremely dry. Scientists think that there may be a small amount of water, in the form of ice, at the planets poles. The poles never receive direct sunlight.

a liquid metal core

Figure 25.10 shows a diagram of Mercurys interior. Mercury is one of the densest planets. Scientists think that the interior contains a large core made mostly of melted iron. Mercurys core takes up about 42% of the planets volume. Mercurys highly cratered surface is evidence that Mercury is not geologically active.

mercury

Mercury is the smallest planet. It has no moon. The planet is also closest to the Sun and appears in Figure 25.7. As Figure 25.8 shows, the surface of Mercury is covered with craters, like Earths Moon. The presence of impact craters that are so old means that Mercury hasnt changed much geologically for billions of years. With only a trace of an atmosphere, it has no weather to wear down the ancient craters. Because Mercury is so close to the Sun, it is difficult to observe from Earth, even with a telescope. The Mariner 10 spacecraft did a flyby of Mercury in 19741975, which was the best data from the planet for decades. In 2004, the MESSENGER mission left Earth. On its way to Mercury it did one flyby of Earth, two of Venus and three of Mercury. In March 2011, MESSENGER became the first spacecraft to enter an orbit around Mercury. During its year-long mission, the craft will map the planets surface and conduct other studies. One of these images can be seen in Figure 25.9.

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short year long days

Mercury is named for the Roman messenger god. Mercury was a messenger because he could run extremely fast. The Greeks gave the planet this name because Mercury moves very quickly in its orbit around the Sun. Mercury orbits the Sun in just 88 Earth days. Mercury has a very short year, but it also has very long days. Mercury rotates slowly on its axis, turning exactly three times for every two times it orbits the Sun. Therefore, each day on Mercury is 58 Earth days long.

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is there water on mars

Water on Mars cant be a liquid. This is because the pressure of the atmosphere is too low. The planet does have a lot of water; it is in the form of ice. The south pole of Mars has a very visible ice cap. Scientists also have evidence that there is also a lot of ice just under the Martian surface. The ice melts when volcanoes erupt. At this times liquid water flows across the surface. Scientists think that there was once liquid water on the planet. There are many surface features that look like water- eroded canyons. The Mars rover collected round clumps of crystals that, on Earth, usually form in water. If there was liquid water on Mars, life might have existed there in the past.

earths motions and moon

Earth rotates on its axis once every 24 hours. This is the length of an Earth day. Earth orbits the Sun once every 365.24 days. This is the length of an Earth year. Earth has one large moon. This satellite orbits Earth once every 29.5 days. This moon is covered with craters, and also has large plains of lava. The Moon came into being from material that flew into space after Earth and a giant asteroid collided. This moon is not a captured asteroid like other moons in the solar system.

venus

Named after the Roman goddess of love, Venus is the only planet named after a female. Venus is sometimes called Earths sister planet. But just how similar is Venus to Earth? Venus is our nearest neighbor. Venus is most like Earth in size.

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a harsh environment

Viewed through a telescope, Venus looks smooth and featureless. The planet is covered by a thick layer of clouds. You can see the clouds in pictures of Venus, such as Figure 25.11. We make maps of the surface using radar, because the thick clouds wont allow us to take photographs of the surface of Venus. Figure 25.12 shows the topographical features of Venus. The image was produced by the Magellan probe on a flyby. Radar waves sent by the spacecraft reveal mountains, valleys, vast lava plains, and canyons. Like Mercury, Venus does not have a moon. Clouds on Earth are made of water vapor. Venuss clouds are a lot less pleasant. They are made of carbon dioxide, sulfur dioxide and large amounts of corrosive sulfuric acid! The atmosphere of Venus is so thick that the pressure on the surface of Venus is very high. In fact, it is 90 times greater than the pressure at Earths surface! The thick atmosphere causes a strong greenhouse effect. As a result, Venus is the hottest planet. Even though it is farther from the Sun, Venus is much hotter even than Mercury. Temperatures at the surface reach 465C (860F). Thats hot enough to melt lead!

plate tectonics

The Earth is divided into many plates. These plates move around on the surface. The plates collide or slide past each other. One may even plunge beneath another. Plate motions cause most geological activity. This activity includes earthquakes, volcanoes, and the buildup of mountains. The reason for plate movement is convection in the mantle. Earth is the only planet that we know has plate tectonics.

instructional diagrams

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questions

hottest of all the planets in the solar system

a. Mercury

b. Opportunity

c. Mars

d. inner planet

e. Earth

f. Messenger

-->  g. Venus

What explains the number of impact craters on Mercury?

a. It is very close to the Sun.

b. The craters have been overrun by lava flows.

-->  c. It is not geologically active.

d. It is subject to constant storms.

rover that explored Mars surface

a. Mercury

-->  b. Opportunity

c. Mars

d. inner planet

e. Earth

f. Messenger

g. Venus

The largest volcano in the solar system is a _ volcano a on the planet __.

a. composite; Mars

-->  b. shield; Mars

c. composite; Venus

d. shield; Venus

only planet in the solar system known to have plate tectonics

a. Mercury

b. Opportunity

c. Mars

d. inner planet

-->  e. Earth

f. Messenger

g. Venus

What is true of life on the inner planets?

a. Earths Moon had life in ancient oceans.

b. Venus has microbes beneath its thick atmosphere

c. Mars has ancient fossil microbes

-->  d. There is only life on Earth

Why is Venus the hottest planet?

a. It is closest to the Sun

-->  b. It has a powerful greenhouse effect.

c. It has the most internal heat

d. It spins the fastest.

any of the four planets closest to the sun

a. Mercury

b. Opportunity

c. Mars

-->  d. inner planet

e. Earth

f. Messenger

g. Venus

smallest of all the planets in the solar system

-->  a. Mercury

b. Opportunity

c. Mars

d. inner planet

e. Earth

f. Messenger

g. Venus

Evidence for liquid water in the Martian past includes

-->  a. water-eroded canyons

b. fossil fish

c. the presence of polar ice currently

d. all of these

spacecraft that is orbiting and studying Mercury

a. Mercury

b. Opportunity

c. Mars

d. inner planet

e. Earth

-->  f. Messenger

g. Venus

planet with the largest volcano in the solar system

a. Mercury

b. Opportunity

-->  c. Mars

d. inner planet

e. Earth

f. Messenger

g. Venus

All of the inner planets were once geologically active.

-->  a. true

b. false

Venus has the largest greenhouse effect of the inner planets.

-->  a. true

b. false

Venus is the only inner planet with a large moon besides Earth.

a. true

-->  b. false

Besides Earth, the inner planets are all solid.

a. true

-->  b. false

The inner planets spin faster than the outer planets.

a. true

-->  b. false

All of the inner planets

a. have very rapid rotation.

b. have a thick atmosphere.

c. have one or more moons.

-->  d. are solid, dense, and rocky.

Which statement about Mercurys core is false?

-->  a. It is very small.

b. It contains mostly iron.

c. It exists in a molten state.

d. It makes up 42% of Mercurys volume.

Venus has all of the following except

-->  a. moons.

b. valleys.

c. mountains.

d. lava plains.

Which process explains why Venus is very hot?

-->  a. greenhouse effect

b. volcanic activity

c. plate tectonics

d. none of the above

The inner planet with an average surface temperature of 14 C is

a. Mercury.

b. Venus.

-->  c. Earth.

d. Mars.

Mars does not usually have liquid water on its surface because the

-->  a. air of the planets atmosphere is too dense.

b. pressure of the planets atmosphere is too low.

c. temperature of the planets surface is too high.

d. two of the above

The largest canyon in the solar system is found on

-->  a. Mars.

b. Earth.

c. Venus.

d. Mercury.

None of the inner planets of the solar system has rings.

-->  a. true

b. false

Compared with the outer planets, the inner planets spin more quickly.

a. true

-->  b. false

All of the inner planets are made of cooled igneous rock.

-->  a. true

b. false

Each year on Mercury lasts just 58 Earth days.

a. true

-->  b. false

Most of Mercury is extremely wet.

a. true

-->  b. false

Clouds on Venus contain sulfur.

-->  a. true

b. false

A day on Venus is longer than a year on Venus.

-->  a. true

b. false

Life could evolve on Earth because its atmosphere contained oxygen.

a. true

-->  b. false

Some features on Mars surface look as though they were eroded by water.

-->  a. true

b. false

Mars moons were meteorites that were captured by Martian gravity.

a. true

-->  b. false

diagram questions

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